194. The effect of undercorrection on distal junctional kyphosis in adult cervical deformity patients

Abstract

<h3>BACKGROUND CONTEXT</h3> Distal junctional kyphosis (DJK) development after cervical deformity (CD) corrective surgery is a growing concern for surgeons and patients. Although proper realignment is known to help mitigate the development of DJK, there has yet to be a study that critically analyzes under correction in certain parameters and the effects on development of DJK. <h3>PURPOSE</h3> To determine the effects of under correction in the development of DJK. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study of single-center database. <h3>PATIENT SAMPLE</h3> This study included 195 CD patients. <h3>OUTCOME MEASURES</h3> Complications; radiographic parameters; HRQL metrics (NDI, EQ5D, mJOA, NRS Neck). <h3>METHODS</h3> Inclusion criteria: operative CD patients (cervical kyphosis >10°, with cSVA>4cm or CBVA>25°) and >18yrs with up to 2-year radiographic and HRQL follow-up. Significant differences in surgical, radiographic, and clinical factors and outcomes were determined. Under correction was defined by a deformity in TS-CL or cSVA Ames Modifier. Moderate Ames cervical lordosis deformity (CL) was TS-CL >15 and high >20, high cSVA deformity was >8cm. <h3>RESULTS</h3> A total of 195 CD patients met inclusion criteria (58.3yrs, 46% Female, 28.3 kg/m2). Overall, 40 (21%) of these patients developed DJK. At baseline patients presented with the following radiographic profile: PT (18.3), PI-LL (-.65), SVA C7-S1 (-6.54), cSVA C2-C7 (9.7), and TS-CL (24). Patients undercorrected in TS-CL developed DJK at a greater rate (28% vs 15%, p=.02), and patients undercorrected in cSVA developed more DJK (65% vs 16%) and underwent more reoperations (42% vs 17%, both p<0.05). Controlling for baseline deformity, frailty and age, patients who maintained a high cSVA deformity had a 3.2 times higher likelihood of developing DJK (3.2[1.6-6.8], p=.002). Patients with a postoperative moderate CL deformity had a 1.8 times higher likelihood of DJK (1.8[.9-3.8], p=.105), and with a high CL deformity, a 2.8 times higher likelihood (2.8[1.1-7.2], p=.03). Controlling for the same factors, patients who remained undercorrected in both cSVA and TS-CL had a 6 times times higher likelihood of developing DJK (6[1.9-17], p=.002). Using CIT to find a threshold cutoff, the risk of DJF was considerably increased for patients with a TS-CL greater than 13.5, (2.4[1.14-5], p=.026), and a cSVA deformity greater than 6cm (3.2[1.5-6.6], p=.026). Patients who were adequately corrected in cSVA and undercorrected in TS-CL demonstrated no significant increased vulnerability to DJK, (p>0.05). <h3>CONCLUSIONS</h3> The TS-CL and cSVA components of Ames criteria show a strong correlation with development of distal junctional kyphosis (DJK). Thresholds for DJK development suggests even patients who fall into a mild deformity as per the Ames criteria are still at an increased risk, and more strict alignment goals may further prevent mechanical failure. cSVA was found to be the dominant radiographic parameter impacting DJK development. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.